Question: For a given input value $a$, the function $f$ outputs a value $b$ to satisfy the following equation. $-3a+6b=a+4b$ Write a formula for $f(a)$ in terms of $a$. $f(a)=$
$f(a)$ expresses $b$ as a function of $a$. To arrive at a correct formula, all we have to do is solve the equation for $b$. $ \begin{aligned}-3a+6b&=a+4b\\\\ 2b&=4a\\\\ b&=\dfrac{4a}{2}\\\\ b&=2a\end{aligned}$ Therefore, this formula expresses $f$ as a function of $a$ : $ f(a)=2a$